1. Field of the Invention
This invention relates to a clarified konjac which comprises konjac-derived glucomannan that is substantially free of insoluble impurities, has a reduced nitrogen content, and has a reduced aqueous sol turbidity potential; as well as sols and gels prepared therefrom.
2. Statement of Related Art
Konjac (Amorphophallus konjac) is a plant, the tuber of which is the source of a well-known foodstuff in China and Japan, namely konjac flour. This flour, which contains a variety of insoluble materials described below as well as a major amount of desirable water-soluble substances, comprises a highly viscous sol of glucomannan and soluble starches when reconstituted in water. The principal soluble constituent is glucomannan, which is useful as an ingredient in various foodstuffs, as well as in industrial applications such as films, oil drilling fluids, and paints.
There are numerous impurities in crude (native, unclarified) konjac flour, principally insoluble starches, cellulose, and nitrogen-containing materials, including proteins, many of which impurities are derived from "sacs" which encapsulate the konjac flour in the tuber. As a result, the sols and gels of crude konjac flour have a highly turbid, milky-white or cloudy appearance (due to water-swollen particulate impurities).
U.S. Pat. No. 3,928,322 to Sugiyama et al. (and U.S. Pat. No. 3,973,008, which is cumulative thereto) disclose a method for producing konjac mannan polysaccharide, that is, glucomannan, which comprises the principal ingredient of konjac flour, from raw konjac flour by first removing insoluble components from an aqueous konjac flour sol by filtration or other conventional means, thereafter dialyzing the sol and subjecting the resulting liquid to freeze-drying to obtain a turbid, cotton-like, low density fibrous product which is hard to grind and poorly soluble in water.
Japanese Application No. 01-49657, filed Mar. 1, 1989, discloses a konjac mannan which has a nitrogenous component of not more than 0.2%. However, the method of achieving this reduced nitrogen content is not disclosed.
U.S. Pat. No. 2,144,522 teaches a method for decolorizing and clarifying galactomannan gum sols such as locust bean gum which comprises contacting the gum sol with activated carbon in the presence of aluminum sulfate, the latter being added in amounts sufficient to form a double Al--Na salt with sodium sulfate which is intrinsically present in the activated carbon itself.
U.S. Pat. No. 3,346,556 discloses a method for preventing the degradation of galactomannan gums such as locust bean gum resulting from heat or pH changes which comprises adding to aqueous gum sols polar organic oxygen-containing hydrophilic stabilizers such as alcohols, glycols, ketones or the like. Incidental to this process there is disclosed in one example (Example 5) a means of clarifying locust bean gum by the conventional use of a filter aid such as diatomaceous earth.
Japanese Patent Disclosures 59-227,267 (Dec. 20, 1984), and 58-165,758 (Sep. 30, 1983) disclose methods for treating aqueous sols of crude konjac flour with certain salts at pH's of 10 or below to obtain an insoluble form of konjac, principally for use as insoluble food products.
Japanese Patent Disclosure 63-68054 (Mar. 26, 1988), discloses a reversibly soluble konjac gel product, but not the removal of insolubles which remain present in the product.